All police interviews are conducted under police caution. In simple terms how I explain the three parts:
1) You have the legal right to remain silent- you do not have to answer police questions
2) However if you do not answer the questions today, and IF the mater later goes to court, and you say something THEN, that you did not say today- the court is less likely to believe you and it could harm your defence
3) The court will know what you've said as the interview will be recorded visually and audibly.
She responded to the line of enquiry initially by giving a written statement. It's hard to answer specific questions if you are in fact innocent and have no detailed knowledge of the charge in question at he time of sudden arrest. Ive no doubt Sturgeon was shocked as she was lead out of her house, put in a. cell to await arrival of a solicitor and having fingerprints, photo and possibly DNA taken.
It's much better at that stage, with such a forensic charge, that is going to rely on detailed documentary evidence to give an initial statement 'I have no knowledge of" etc. The police always then respond along the lines of - "please, go away and think of any evidence that would exonerate you, whatever you can think of- texts, emails, witness statements in support, budge statements etc etc and please get in touch further...."
This she appeared to do, following up with a further detailed written statement. I feel strongly it is unfair to say she did not co operate with Police Scotland in that context or to suggest saying "no comment" attached with a written statement, is proof of culpability. It is not.